1. Technical Field
The present invention relates generally to cellular wireless communication networks; and more particularly to the transmission of voice communications and data communications in such a cellular wireless communication network.
2. Related Art
Wireless networks are well known. Cellular wireless networks support wireless communication services in many populated areas of the world. Satellite wireless networks are known to support wireless communication services across most surface areas of the Earth. While wireless networks were initially constructed to service voice communications, they are now called upon to support data communications as well.
The demand for data communication services has exploded with the acceptance and widespread use of the Internet. While data communications have historically been serviced via wired connections, wireless users are now demanding that their wireless units also support data communications. Many wireless subscribers now expect to be able to “surf” the Internet, access their email, and perform other data communication activities using their cellular phones, wireless personal data assistants, wirelessly linked notebook computers, and/or other wireless devices. The demand for wireless network data communications will only increase with time. Thus, wireless networks are currently being created/modified to service these burgeoning data communication demands.
Significant performance issues exist when using a wireless network to service data communications. Wireless networks were initially designed to service the well-defined requirements of voice communications. Generally speaking, voice communications require a sustained bandwidth with minimum signal-to-noise ratio (SNR) and continuity requirements. Data communications, on the other hand, have very different performance requirements. Data communications are typically bursty, discontinuous, and may require a relatively high bandwidth during their active portions. To understand the difficulties in servicing data communications within a wireless network, consider the structure and operation of a cellular wireless network.
Cellular wireless networks include a “network infrastructure” that wirelessly communicates with user terminals within a respective service coverage area. The network infrastructure typically includes a plurality of base stations dispersed throughout the service coverage area, each of which supports wireless communications within a respective cell (or set of sectors). The base stations couple to base station controllers (BSCs), with each BSC serving a plurality of base stations. Each BSC couples to a mobile switching center (MSC). Each BSC also typically directly or indirectly couples to the Internet.
In operation, a user terminal communicates with one (or more) of the base stations. A BSC coupled to the serving base station routes voice communications between the MSC and the serving base station. The MSC routes the voice communication to another MSC or to the public switched telephone network (PSTN). BSCs route data communications between a servicing base station and a packet data network that may couple to the Internet.
The wireless link between the base station and the user terminal is defined by one of a plurality of operating standards, e.g., AMPS, TDMA, CDMA, GSM, etc. These operating standards, as well as new 3G and 4G operating standards define the manner in which the wireless link may be allocated, setup, serviced and torn down. These operating standards must set forth operations that will be satisfactory in servicing both voice and data communications.
The wireless network infrastructure must support both low bit rate voice communications and the higher bit rate data communications. More particularly, the network infrastructure must transmit low bit rate, delay sensitive voice communications together with high data rate, delay tolerant rate data communications. While voice communications typically have a long hold time, e.g., remain active for longer than two minutes on the average, high data rate/delay tolerant data communications are bursty and are active only sporadically. As contrasted to the channel allocation requirements of voice communications, channels must be frequently allocated and deallocated to the data communication in order to avoid wasting spectrum. Such allocation and deallocation of channels to the data communications consumes significant overhead.
To increase throughput of conventional cellular wireless networks, the allocated frequency spectrum is oftentimes subdivided into a plurality of sub-spectrums, each of which is serviced by a respective carrier. With such a subdivision, the number of user terminals that may be serviced increases relative to the number that may be serviced by a single carrier. Further, multicarrier systems are less sensitive to dispersion and frequency selective fading. Thus, gains are achieved in systems of this type by servicing a greater number of user terminals at any given time. Further, the overhead consumed in allocating/deallocating channels significantly may also decrease in a system of this type since a greater number of user terminals may be serviced at any one time. However, the bandwidth available for communications on each carrier is less than it would be for a single carrier using the full spectrum. Thus, the gains achieved in reducing allocation/deallocation overhead are offset by reduced throughput.
It would therefore be desirable to provide a communication system that efficiently uses a plurality of carriers to service communications with minimal waste of spectral capacity. Further, it would also be desirable to provide a communication system that services both delay sensitive low bit rate voice communications and delay tolerant data communications upon a plurality of carriers without requiring significant additional overhead resources.